1. Field of the Invention
The present invention relates to a layout design system of semiconductor integrated circuits facilitating an automatic selection of a wiring pattern by use of CAD, and more particularly to a layout design system of semiconductor integrated circuits for designing a terminal layout of an oblique wiring pattern, a layout design method, and a layout design program. The present invention further relates to a manufacturing method of semiconductor integrated circuits using the layout design system, layout design method and layout design program.
2. Description of the Related Art
Progress of LSI technologies makes the circuit scale larger, and this causes an increase in an amount of logic design computations for the circuit. Accordingly, as a logic design method capable of effectively utilizing computers, a logic design by use of Computer Aided Design (CAD) has been carried out.
In designing interconnection of basic horizontal and vertical lines in the orthogonal coordinate system on CAD, horizontal and vertical lines often terminate at an intersection point of two or more orthogonal lines. When the horizontal lines and the vertical lines are formed in different levels in an actual semiconductor device, a via hole must be formed at the terminal portions of the metal lines to connect the horizontal and vertical lines three-dimensionally. As a matter of course, a connection pattern corresponding to the via hole must be defined at the terminal portions of the horizontal and vertical lines even in a layout by use of CAD.
Generally, if two basic orthogonal lines having an ordinary width W terminate at an intersection, wire terminating process is carried out to extend the ends of the orthogonal lines by W/2.
FIGS. 1A to 1E illustrate an example of the wire terminating process of the basic orthogonal lines of the minimum width. In FIG. 1A, a horizontal line 901 and a vertical line 903 intersect each other and terminate there. In a CAD system, only the intersection point at which the center lines 902 and 904 of the respective lines intersect each other is recognized as an intersection point 908. The CAD system does not recognize the overlap of the two orthogonal lines at all.
When, in an actual semiconductor device, the horizontal line 901 is formed in a lower level and the vertical line 902 is formed in an upper level, these two lines must be connected three-dimensionally by use of a via hole. As a matter of course, the CAD layout requires a connection pattern 905 for connecting the two lines. The connection pattern 905 has a bottom metal 901a, which is a part of the end portion of the line 901 in the lower level, a top metal 903a, which is a part of the end portion of the line 903 in the upper level, and an opening pattern (hereinafter, referred to as a “cut pattern” or simply as a “cut”) 907 for connecting the top and bottom metals 903a and 901a. 
In the example of FIGS. 1A to 1E, since the CAD recognizes that the two lines intersect each other, it is possible to define the connection pattern 905 at the intersection point 908 on the layout. However, since an overlapped area where the horizontal and vertical lines 901 and 903 overlap is very small in the state of FIG. 1A, even when the via hole is formed based on the connection pattern 905 in the actual semiconductor integrated circuit, the connections of the upper and lower levels and the via hole cannot be achieved successfully.
To overcome this problem, in the design system of the semiconductor integrated circuits, the ends of the horizontal and vertical lines 901 and 903 are respectively extended by W/2, as shown in FIG. 1B, so that the two lines completely overlap at their end portions. Then, wire terminating process is carried out so as to place the connection pattern 905 on the overlapped area, as shown in FIG. 1C.
FIG. 1D illustrates the shape of the connection pattern 905 at the end portion of the basic orthogonal lines at which they intersect each other, when viewed from above. Since the connection pattern 905 is placed on the intersection of the basic orthogonal lines, the connection pattern 905 has a square shape when viewed from above. FIG. 1E is a side view of the shape of the connection pattern 905. The lower metal 901a and the upper metal 903a are connected by the cut 907.
FIG. 2 illustrates another example of wire terminating process of two orthogonal lines having wide widths. In this case, the two wider orthogonal lines intersect and terminate at the intersection point. These wider lines are special lines such as a power source line and a clock line, and subjected to a wire terminating process similarly to general signal lines. A connection pattern 915 is placed on an overlapped area where a wider horizontal line 911 and a wider vertical line 913 intersect. At this time, since the overlapped area is made wider, a plurality of cuts 917 are provided in one connection pattern. Also in this case, both of the horizontal and vertical lines 911 and 913 are extended by W/2, and a metal pattern completely including the connection pattern 915 having the plurality of cuts 917 is placed in the overlapped area.
It is easy for the CAD system to carry out the wire terminating process to design interconnection consisting of only basic orthogonal lines in the horizontal and vertical directions, as in the examples shown in FIGS. 1 and 2.
However, as the configuration of semiconductor integrated circuits is made finer, higher precision is required in every respect including a manufacturing process and components of a semiconductor integrated circuit. Particularly, a delay component caused by an interconnection (or a wiring) significantly affects the performance of the integrated circuit as the integrated circuit is made finer. Therefore, it is an important subject how to reduce such a delay in the integrated circuit.
Most of the delay components of the interconnection are caused by a line resistance. The most effective way to reduce the line resistance is to reduce a line length. Accordingly, it has been proposed to use oblique lines, in addition to the basic orthogonal lines extending in the horizontal and vertical directions, to reduce the distance between two points in a semiconductor circuit. There is also a proposal to design a circuit layout using oblique lines on CAD. In this case, as the lines including the oblique lines are made in the form of multi-level structure composed of a larger number of levels, for example, the shape and the forming process of via holes connecting basic orthogonal lines in a lower level and oblique lines in an upper level must be contrived.
The inventors of the present invention have proposed in U.S. patent application Ser. No. 09/338,593 a technique for greatly reducing a line resistance of oblique lines itself. This is achieved by setting the width and film thickness of the oblique line to 21/2 times as large as those of the basic orthogonal lines. In this gazette, a technology for fully securing a cut area by contriving the shape of a via hole connecting metal lines of different levels is also proposed. In order to realize a high-speed operation of an integrated circuit, the inventors also proposed a tree-type clock supply line path comprised of a combination of oblique lines and the basic orthogonal lines. FIG. 3 illustrates a line structure using the oblique lines. As shown in FIG. 3, considered is the line structure having a horizontal first-level metal line 921, a vertical second-level metal line 922, a horizontal third-level metal line 923, an oblique fourth-level metal line 924, and a fifth-level metal line 925 perpendicular to the fourth-level metal line 924. When the first-level metal line 921, the second-level metal line 922 and the third-level metal line 923 have a line width W, respectively, the fourth-level metal line 924 and the fifth-level metal line 925 have a line width of 21/2W.
The inventors of the present invention have proposed a wire terminating process method for lines on a layout in U.S. patent application Ser. No. 09/771,050 when oblique lines are used. FIGS. 4A to 4C illustrate the wire terminating process for an oblique line. As shown in FIG. 4A, when a horizontal line 941 of a minimum line width extending in the horizontal direction is generated and an oblique line 943 having a line width 21/2 times as wide as that of the horizontal line 941 and extending at an oblique angle relative to the horizontal line 941 is generated, a cut 947 is provided. FIG. 4B is a drawing when the cut 947 is viewed from above, and FIG. 4C is a drawing when the cut 947 is viewed laterally. FIGS. 5A, 5B and 5C illustrate an intersection structure of a line with a minimum line width in the oblique line. As shown in FIG. 5A, when a horizontal line 941 is generated in a lower level and an oblique line 943 is generated in an upper level, a connection pattern (via) 945 is provided. At this time, a wire terminating process so as to delete a metal at a shaded area is carried out. FIG. 5B is a drawing when the connection pattern (via) 945 is viewed from above, and FIG. 5C is a drawing when the connection pattern (via) 945 is viewed laterally. At this time, the connection pattern 945 has an upper metal portion 943a having a parallelogram shape and a lower metal portion 941a having a rectangular shape.
On the other hand, in the line layout system, there has been one basic VIA shape using the line for each technology. Alternatively, a large VIA using one basic VIA shape (for example, a rectangular shape is typical) in plural has been defined or automatically generated.
However, in the line layout method using an oblique line, a wide line space is consumed when a line is bent in the same line level, and hence there has been a problem that a degree of line integration is lowered and a data amount in a mask generation operation increases.
Moreover, in consideration for various line layout methods, the necessity to selectively perform an optional VIA in accordance with a line pattern and to perform a wire terminating process suitable for the respective VIA shapes has been arisen.